U.S. patent number 9,550,145 [Application Number 14/680,729] was granted by the patent office on 2017-01-24 for exhaust gas treatment apparatus, ship, and exhaust gas treatment method.
This patent grant is currently assigned to FUJI ELECTRIC CO., LTD.. The grantee listed for this patent is FUJI ELECTRIC CO., LTD.. Invention is credited to Tadashi Komatsu, Kuniyuki Takahashi.
United States Patent |
9,550,145 |
Takahashi , et al. |
January 24, 2017 |
Exhaust gas treatment apparatus, ship, and exhaust gas treatment
method
Abstract
An exhaust gas treatment apparatus and method that absorbs gas
by bringing the gas and a liquid into contact with each other has a
plurality of scrubbers that each include an absorption tower main
unit in which an internal space is formed. A spray apparatus sprays
liquid in a predetermined vertical region of the internal space,
and a gas supply apparatus introduces the gas into the absorption
tower main unit. A number of first passages branch from a pipe
supplying the liquid to the exhaust gas treatment apparatus and are
connected to the spray apparatuses of the scrubbers. A number of
second passages branch from a pipe supplying the gas to the exhaust
gas treatment apparatus and are connected to the gas supply
apparatuses of the scrubbers.
Inventors: |
Takahashi; Kuniyuki (Hino,
JP), Komatsu; Tadashi (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI ELECTRIC CO., LTD. |
Kawasaki-shi |
N/A |
JP |
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Assignee: |
FUJI ELECTRIC CO., LTD.
(Kawasaki-Shi, JP)
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Family
ID: |
51731310 |
Appl.
No.: |
14/680,729 |
Filed: |
April 7, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150209723 A1 |
Jul 30, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2014/060177 |
Apr 8, 2014 |
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Foreign Application Priority Data
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Apr 17, 2013 [JP] |
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2013-086290 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D
53/18 (20130101); B01D 53/346 (20130101); B01D
53/78 (20130101); B63H 21/32 (20130101); B01D
53/504 (20130101); B01D 2259/4566 (20130101); B01D
2251/304 (20130101); B01D 2252/1035 (20130101); B01D
2258/0283 (20130101); B01D 2252/10 (20130101) |
Current International
Class: |
F01N
3/08 (20060101); B01D 53/50 (20060101); B01D
53/34 (20060101); B63H 21/32 (20060101); B01D
53/78 (20060101); B63B 17/06 (20060101); B01D
53/18 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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202191840 |
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Apr 2012 |
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CN |
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10 2010 042 419 |
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Apr 2012 |
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DE |
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S47-21369 |
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Oct 1972 |
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JP |
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H09-192447 |
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Jul 1997 |
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JP |
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3073972 |
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Aug 2000 |
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JP |
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2002-136829 |
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May 2002 |
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JP |
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2009-240908 |
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Oct 2009 |
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JP |
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2014-200735 |
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Oct 2014 |
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JP |
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Other References
Chinese Office Action with translation dated Oct. 27, 2015. cited
by applicant .
Japanese Office Action dated Mar. 1, 2016 and its partial
translation. cited by applicant.
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Primary Examiner: Vanoy; Timothy
Attorney, Agent or Firm: Rabin & Berdo, P.C.
Parent Case Text
This application is a continuation under 35 U.S.C. 120 of
International Application PCT/JP2014/060177 having the
International Filing Date of Apr. 8, 2014 which claims foreign
prior benefits of Japanese Patent Application No. 2013-086290 filed
on Apr. 17, 2013. The subject matter disclosed in these identified
applications is incorporated herein by reference.
Claims
What is claimed is:
1. An exhaust gas treatment apparatus that processes gas by
bringing liquid into contact with it, comprising: a plurality of
scrubbers that include an absorption tower main unit, a spray
apparatus that sprays liquid in the absorption tower main unit, and
a gas supply apparatus that supplies the gas to be processed into
the absorption tower main unit; a plurality of first passages that
branch from a pipe supplying said liquid to the treatment
apparatus, and that is connected to the spray apparatus of each of
the plurality of scrubbers; and a plurality of second passages that
branch from a pipe supplying said gas to the treatment apparatus,
and that is connected to the gas supply apparatus of each of the
plurality of scrubbers.
2. The exhaust gas treatment apparatus according to claim 1,
wherein a switching valve is disposed in each of the plurality of
first passages and the plurality of second passages, the treatment
apparatus further comprising a controller that controls switching
of the switching valves.
3. The exhaust gas treatment apparatus according to claim 2,
wherein the gas in an exhaust gas from an engine and the controller
controls a total number of scrubbers to be operated by controlling
switching of the switching valves, said total number being
determined based on an engine load instruction.
4. The exhaust gas treatment apparatus according to claim 3,
wherein the controller controls an amount of the liquid being
sprayed in the plurality of scrubbers based on at least one of a
load factor of the engine and an amount of the exhaust gas to be
processed.
5. The exhaust gas treatment apparatus according to claim 4,
wherein the controller implements control so as to increase a total
number of the scrubbers to be operated when at least one of the
load factor of the engine and the amount of the exhaust gas to be
processed increases, and decrease a total number of scrubbers in
operation when at least one of the load factor of the engine and
the amount of the exhaust gas to be processed decreases.
6. The exhaust gas treatment apparatus according to claim 5,
wherein when the controller increases the total number of the
scrubbers to be operated, the controller decreases a flow rate of
the gas being supplied to at least one of the scrubbers in
operation.
7. The exhaust gas treatment apparatus according to claim 5,
wherein when the controller decreases the total number of the
scrubbers in operation, the controller increases the flow rate of
the exhaust gas being supplied to at least one of the scrubbers
that continue operating thereafter.
8. The exhaust gas treatment apparatus according to claim 3,
wherein the controller controls the flow rate of the exhaust gas
being supplied to one predetermined scrubber among the scrubbers
which are in operation.
9. The exhaust gas treatment apparatus according to claim 6,
wherein when a flow rate of exhaust gas being supplied to a first
scrubber under flow control reaches an upper limit value, the
controller sets a flow rate of exhaust gas to be supplied to a
second scrubber to a predetermined set value and starts operation
of said second scrubber, and decreases the flow rate of the exhaust
gas being supplied to said first scrubbers by said predetermined
set value, and wherein when the flow rate of the exhaust gas being
supplied to said first scrubber reaches the upper limit value
again, the controller starts controlling the flow rate of the
exhaust gas being supplied to said second scrubber.
10. The exhaust gas treatment apparatus according to claim 7,
wherein when a flow rate of exhaust gas being supplied to a first
scrubber under flow control reaches a lower limit value of the flow
rate, the controller keeps the flow rate of the exhaust gas of the
first scrubber to said lower limit value and starts controlling a
flow rate of exhaust gas being supplied to a third scrubber in
operation, and when the flow rate of the exhaust gas being supplied
to the third scrubber reaches the lower limit value, the controller
stops operation of one of the scrubbers in operation at the lower
limit value, and increases the flow rate of the exhaust gas being
supplied to the other scrubber in operation by the lower limit
value.
11. The exhaust gas treatment apparatus according to claim 10,
wherein the absorption tower main unit has a peripheral wall, a
liquid returning member is disposed on the peripheral wall, and the
liquid returning member includes a turn-back surface area that
circularly protrudes from the peripheral wall toward a center axis,
a bent piece that is bent down from an edge of the turn-back
surface area on the center axis side, a liquid collecting wall that
protrudes upward from the edge of the turn-back surface area to
form a liquid reservoir, and an opening that allows the liquid
collected in the liquid reservoir to fall through.
12. The exhaust gas treatment apparatus according to claim 11,
wherein the opening is disposed in a position where a velocity of
the exhaust gas is slower, compared with an area near the
peripheral wall area.
13. The exhaust gas treatment apparatus according to claim 3,
wherein the liquid is seawater, the exhaust gas treatment apparatus
further comprising: a seawater tank that stores the seawater that
is in contact with the exhaust gas as circulating seawater; and an
alkali pump that supplies an alkali agent to the circulating
seawater which is supplied from the seawater tank to the spray
apparatus.
14. The exhaust gas treatment apparatus according to claim 1,
wherein an internal space is formed in the absorption tower main
unit, and the spray apparatus sprays the liquid in a predetermined
vertical region of the internal space.
15. A ship comprising an exhaust gas treatment apparatus for
treating exhaust gas from a ship engine, and that processes the
exhaust gas by bringing liquid into contact therewith, the
apparatus including: a plurality of scrubbers that each include an
absorption tower main unit, a spray apparatus that sprays the
liquid in the absorption tower main unit, and a gas supply
apparatus that supplies the exhaust gas into the absorption tower
main unit; a plurality of first passages that branch from a pipe
supplying said liquid to the exhaust gas treatment apparatus, and
that is connected to the spray apparatus of each of the plurality
of scrubbers; and a plurality of second passages that branch from a
pipe supplying said exhaust gas to the exhaust gas treatment
apparatus, and that is connected to the gas supply apparatus of
each of the plurality of scrubbers.
16. An exhaust gas treatment method, the method comprising the
steps of: distributing exhaust gas to a plurality of scrubbers;
distributing liquid to the plurality of scrubbers; controlling
operation of the plurality of scrubbers by controlling a total
number of scrubbers to be operated among the plurality of
scrubbers, the total number being determined based on an engine
load instruction; and a step of removing toxic substances in the
exhaust gas by bringing the exhaust gas and the liquid into contact
with each other, said exhaust gas and said liquid being supplied to
the plurality of scrubbers respectively.
17. The exhaust gas treatment method according to claim 16, wherein
said distributing the exhaust gas includes distributing the exhaust
gas to the plurality of scrubbers through a plurality of first
passages disposed to each of the plurality of scrubbers, said
distributing the liquid includes distributing the liquid to the
plurality of scrubbers through a plurality of second passages
respectively connected each of the plurality of scrubbers, and said
controlling the total number of scrubbers includes controlling
switching of switching valves each of which is disposed in each of
the first passage and the second passage.
18. The exhaust gas treatment method according to claim 17, wherein
the controlling switching of the switching valves includes
controlling a total number of scrubbers to be operated by
controlling switching of the switching valves based on the engine
load instruction.
19. The exhaust gas treatment method according to claim 18, wherein
the controlling the total number of scrubbers includes controlling
an amount of spray of the liquid to be supplied in the plurality of
scrubbers according to at least one of a load factor of the engine
and an amount of exhaust gas included in an exhaust gas stream.
20. The exhaust gas treatment method according to claim 19, wherein
the controlling the total number of scrubbers includes: increasing
a total number of scrubbers to be operated when at least one of the
load factor of the engine and the amount of exhaust gas included in
an exhaust gas stream to be processed increases, and decreasing a
total number of scrubbers in operation when at least one of the
load factor of the engine and the amount of the exhaust gas
included in the exhaust gas stream decreases.
Description
BACKGROUND
Technical Field
The present invention relates to an exhaust gas treatment
apparatus, a ship and an exhaust gas treatment method for removing
toxic substances (mainly sulfur oxide (SO.sub.x)).
Background Art
As a removal apparatus for removing such toxic substances as
SO.sub.x, nitrogen oxide (NO.sub.x) and particulate matter (PM) in
exhaust gas, an exhaust gas treatment apparatus using a cyclone
scrubber is known (e.g. see Patent Document 1). An exhaust gas
desulfurization apparatus according to Patent Document 1 absorbs or
collects dust by allowing gas, which circles and rises from the
bottom of a cylindrical tower, to contact liquid that is sprayed in
a radius direction of the tower through spray nozzles disposed with
appropriate intervals on a spray pipe, which is installed
vertically on the center axis of the tower.
Patent Document 1: Japanese Patent No. 3073972
SUMMARY OF THE INVENTION
In a cyclone scrubber, the exhaust gas and the absorbing solution
must be separated using the centrifugal force of the exhaust gas
flow, to stop the absorbing solution from splashing through the
exhaust gas outlet of the scrubber. The centrifugal force here is
given by the following Expression (1). F=mv.sub.2/R (1)
On the other hand, in the cyclone scrubber, the rate of removing
the toxic substance from the exhaust gas is higher as the gas
velocity in the vertical direction is slower. To decrease the gas
velocity, it is necessary to increase the cross-sectional area of
the scrubber. If the scrubber has a cylindrical shape, the
cross-sectional area of the scrubber can be increased by increasing
the diameter thereof.
In Expression (1), if the diameter is increased with fixing the
height of the scrubber, the centrifugal force F decreases in
inverse proportion to the radius R. And if the radius R is
increased, the distance from the spray nozzle to the inner wall
face of the scrubber increases, therefore it is more likely that
the absorbing solution sprayed from the spray nozzle will not reach
the inner wall face of the scrubber, and sprays through the exhaust
gas outlet. As a result, it becomes necessary to set an upper limit
value of the diameter for the cyclone scrubber depending on the
conditions.
Further, the cyclone scrubber must be designed so that the assumed
maximum flow rate of the exhaust gas can be treated. On the other
hand, the amount of exhaust gas that is treated by the cyclone
scrubber changes according to the changes in the load on the
exhaust gas generation apparatus. For example, if the amount of the
absorbing solution that can treat the maximum flow rate is sprayed
in the cyclone scrubber when the load on the exhaust gas generation
apparatus has decreased and the amount of exhaust gas to be treated
has decreased, then the capacity [of the cyclone scrubber] becomes
excessive, which generates unnecessary expenses since absorbing
solution and power are wasted. Hence it is desirable for the
cyclone scrubber to change the amount of the absorbing solution
according to the change in the load.
In a cyclone scrubber, however, a number of spray nozzles to spray
the absorbing solution is unchanged, therefore if the amount of the
absorbing solution is decreased, the injection pressure drops and
the spray properties worsen. This means that it is necessary to
configure the cyclone scrubber so that appropriate spray properties
are maintained, regardless the increase/decrease in the amount of
exhaust gas to be treated.
Moreover, to treat exhaust gas having a large flow rate by using
one scrubber that has a cylindrical shape, the diameter of the
scrubber must be large, which makes installability more difficult.
In particular, when the scrubber is installed in a location where
the installation space is limited, such as onboard a ship, the
layout of the installation is a problem.
With the foregoing in view, it is an object of the present
invention to provide an exhaust gas treatment apparatus, a ship,
and an exhaust gas treatment method that allows treating exhaust
gas having a high flow rate, while limiting the diameter of a
scrubber.
In one aspect, the present invention provides an exhaust gas
treatment apparatus that processes exhaust gas by bringing liquid
into contact, including: a plurality of scrubbers that include an
absorption tower main unit, a spray apparatus that sprays liquid in
the absorption tower main unit, and a gas supply apparatus that
supplies exhaust gas into the absorption tower main unit, a
plurality of first passages that branch from a pipe supplying the
liquid to the exhaust gas treatment apparatus, and that is
connected to the spray apparatus of each of the plurality of
scrubbers, and a plurality of second passages that branch from a
pipe supplying the exhaust gas to the exhaust gas treatment
apparatus, and that is connected to the gas supply apparatus of
each of the plurality of scrubbers.
According to the exhaust gas treatment apparatus, a plurality of
scrubbers are installed, and the exhaust gas to be treated can be
distributed to the plurality of scrubbers, and therefore the
removal rate of the toxic substances in the exhaust gas can be
improved in the entire exhaust gas treatment apparatus, while
keeping the diameter of each scrubber to a predetermined value or
less. Moreover, since the diameter of each scrubber can be a
predetermined value or less, splashing of the absorbing solution
can be suppressed.
Further, the installation locations of the scrubbers in the exhaust
gas treatment apparatus can be distributed, hence the exhaust gas
treatment apparatus can be installed in a location that is subject
to limited installation space, such as in an engine room or on the
deck of a ship, and installability of the exhaust gas treatment
apparatus can be improved.
In this exhaust gas treatment apparatus, it is preferable that a
switching valve is disposed in each of the plurality of first
passages and the plurality of second passages, and this exhaust gas
treatment apparatus further includes a controller that controls
switching of the switching valves.
In this case, the liquid to be supplied to the spray apparatus of
the scrubber and the gas to be introduced to the scrubber can be
controlled by controlling the switching of the switching valves,
hence the number of scrubbers to be operated can be changed
depending on the combustion devices that generate exhaust gas and
the changes in the engine load. In other words, the number of
scrubbers to be operated can be adjusted according to the amount of
exhaust gas to be or being treated, hence an energy saving
operation without waste is implemented. (Herein, exhaust gas to be
treated and exhaust gas being treated are used interchangeably and
corresponds to the amount of exhaust gas flowing into the
apparatus).
In this exhaust gas treatment apparatus, it is preferable that the
controller controls the switching of the switching valves and
controls a total number of scrubbers to be operated, based on an
engine load instruction.
In this case, the controller can control an amount of the liquid
being sprayed in the plurality of scrubbers according to the
changes in the engine load or the like, hence appropriate spray
properties can be maintained.
In this exhaust gas treatment apparatus, it is preferable that the
controller controls the total number of the scrubbers to be
operated according to at least one of the load factor of the engine
and the amount of exhaust gas to be treated.
In this exhaust gas treatment apparatus, it is preferable that the
controller controls an amount of the liquid being sprayed in the
plurality of scrubbers according to at least one of the load factor
of the engine and the amount of exhaust gas to be treated.
In this exhaust gas treatment apparatus, it is preferable that the
plurality of scrubbers are cyclone scrubbers, and the diameter of
each cyclone scrubber is a predetermined value or less.
In this exhaust gas treatment apparatus, it is preferable that the
absorption tower main unit has a peripheral wall portion, a liquid
returning member is disposed on the peripheral wall portion, and
the liquid returning member includes: a turn-back surface portion
that circularly protrudes from the peripheral wall portion toward
the center axis; a bent piece that is bent down from the edge of
the turn-back surface portion on the center axis side; a liquid
collecting wall that protrudes upward from the edge of the
turn-back surface portion to form a liquid collecting portion; and
an opening that allows the liquid collected in the liquid
collecting portion to fall through.
In this exhaust gas treatment apparatus, it is preferable that the
opening is disposed in a position where a gas velocity is slower,
compared with an area near the peripheral wall portion.
In this exhaust gas treatment apparatus, it is preferable that the
liquid is seawater, this exhaust gas treatment apparatus further
including: a seawater tank that stores the seawater contacted with
the exhaust gas as circulating seawater; and an alkali pump that
supplies an alkali agent to the circulating seawater which is
supplied from the seawater tank to the spray apparatus.
A ship, according to the present invention, has any one of the
exhaust gas treatment apparatuses described above on board.
In one aspect, an exhaust gas treatment method of the present
invention has: distributing exhaust gas to a plurality of
scrubbers, distributing liquid to the plurality of scrubbers,
controlling operation of the plurality of scrubbers, based on an
engine load instruction, and a step of removing toxic substances in
the exhaust gas by bringing the exhaust gas and the liquid into
contact with each other, the exhaust gas and the liquid being
supplied to the plurality of scrubbers respectively.
According to the present invention, the exhaust gas treatment
apparatus can allow treating exhaust gas having a high flow rate
while limiting the diameter of each absorption tower.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram depicting an exhaust gas treatment system
centering around a scrubber according to the present
embodiment;
FIG. 2A is a top view of the scrubber, and FIG. 2B is a
cross-sectional view of the scrubber;
FIG. 3 is a diagram depicting a configuration of an exhaust gas
treatment apparatus according to the present embodiment;
FIG. 4 is a graph depicting a relationship between the number of
scrubbers to be operated and an engine load or amount of exhaust
gas to be treated; and
FIG. 5 is a graph depicting a relationship between a flow rate per
scrubber and an engine load or amount of exhaust gas treated.
DETAILED DESCRIPTION
Embodiments of the present invention will now be described in
detail with reference to the accompanying drawings.
FIG. 1 is a diagram depicting an exhaust gas treatment system
centering around a scrubber according to the present embodiment. A
system, which removes sulfur dioxide (SO.sub.2) contained in
exhaust gas discharged from an engine of a ship, is considered as
the exhaust gas treatment system according to the present
embodiment. The discharge gas treatment system according to the
present embodiment, however, is not limited to this, but can be
applied to the treatment of various exhaust gases constituting such
substances as nitrogen oxide and sulfur oxide.
As illustrated in FIG. 1, the exhaust gas treatment system is
constituted mainly by a scrubber 10 to which exhaust gas is
supplied from the engine 20, a seawater pump unit 30 that includes
a seawater pressure pump and a seawater drain pump, a drainage tank
40, and a filter unit 50 that filters drainage.
The exhaust gas discharged from the engine 20 is introduced to the
scrubber 10. The exhaust gas includes 50 to 1500 ppm of sulfur
dioxide (SO.sub.2). In the process of this exhaust gas rising
inside the scrubber 10, seawater introduced into the scrubber 10
via the seawater pump unit 30 is sprayed so that the gas and the
liquid contact.
The sulfur dioxide in the exhaust gas is absorbed and removed by
the seawater (alkali), as shown in Expressions (2) and (3).
SO.sub.2+NaHCO.sub.3.fwdarw.NaHSO.sub.3+CO.sub.2 .uparw. (2)
NaHSO.sub.3+NaHCO.sub.3+1/2O.sub.2.fwdarw.Na.sub.2SO.sub.4+H.sub.2O+CO.su-
b.2.uparw. (3) And Expressions (4) and (5) show the case when the
sulfur dioxide in the exhaust gas is absorbed and removed by sodium
hydroxide (NaOH). SO.sub.2+NaOH.fwdarw.NaHSO.sub.3 (4)
NaHSO.sub.3+NaOH+1/2O.sub.2.fwdarw.Na.sub.2SO.sub.4+H.sub.2O
(5)
The exhaust gas from which the sulfur dioxide has been removed is
exhausted into air through the upper portion of the scrubber
10.
The seawater sprayed inside the scrubber 10 drips down along the
inner wall face of the scrubber 10 by its own weight, and is stored
in the storage disposed in a lower portion of the scrubber 10 as a
liquid reservoir. The stored seawater is drained into the drainage
tank 40 via the seawater pump unit 30, is then filtered by the
filter unit 50, and drained into the sea.
Now the configuration of the scrubber 10 according to the present
embodiment will be described in concrete terms. FIG. 2A is a top
view of the scrubber 10 according to the present embodiment, and
FIG. 2B is a cross-sectional view of this scrubber 10.
As illustrated in FIG. 2, the scrubber 10 has: an absorption tower
main unit 11 in which an internal space is formed in the vertical
direction; a spray apparatus 12 that sprays liquid as mist in a
predetermined vertical region of the internal space of the
absorption tower main unit 11; a gas supply apparatus 13 that
introduces gas into the absorption tower main unit 11 from a
position lower than the region where the spray apparatus 12 sprays
the liquid; a liquid returning member 14 which is disposed in a
position higher than the region where the spray apparatus 12 sprays
the liquid, and circularly protrudes from the inner wall face of
the absorption tower main unit 11 toward the center axis, and of
which edge on the center axis side is bent at least downward; and a
baffle 15 which is disposed in a position lower than the spray
apparatus 12. The spray apparatus 12 is connected to the seawater
pump unit 30 shown in FIG. 1, and the gas supply apparatus 13 is
connected to the engine 20 shown in FIG. 1.
The absorption tower main unit 11 is constituted by a cylindrical
peripheral wall area 11a and a circular base wall area 11b. The
peripheral wall area 11a is formed so that the diameter thereof is
always the same. The upper end of the peripheral wall area 11a is
open, where an opening 11c is formed. In this embodiment the
absorption tower main unit 11 is cylindrical, but the shape of the
absorption tower main unit 11 is not limited to this, and may be a
prism, for example.
The spray apparatus 12 is disposed on the center axis of the
absorption tower main unit 11. The spray apparatus 12 includes: a
feed pipe 12a which is inserted into the absorption tower main unit
11 from outside the absorption tower main unit 11, and extends to
the center position of the absorption tower main unit 11; a conduit
12b which is a main pipe connected to the insertion end of the feed
pipe 12a, and extends toward a predetermined vertical region of the
internal space of the absorption tower main unit 11; branch pipes
12c which are connected to the conduit 12b, and extend toward the
peripheral wall area 11a of the absorption tower main unit 11; and
a spray nozzle 12d which is disposed at the tip of each branch pipe
12c, and sprays liquid supplied through the branch pipe 12c in a
predetermined range. Each spray nozzle 12d is installed so that the
angle formed by the long direction of the branch pipe 12c and the
center line of the spray region of the spray nozzle 12d is an acute
angle, as described later.
The branch pipes 12c, which are arranged vertically in a plurality
of levels, are disposed such that adjacent branch pipes 12c
intersect orthogonally in the vertical direction. The arrangement
of the branch pipes 12C, with respect to the conduit 12b, is not
limited to this, and four branch pipes 12c may be disposed on a
same circumference of the conduit 12b at 90.degree. intervals. The
material of the spray nozzle 12d is preferably austenite stainless
steel material that has corrosion resistance in the case of using
seawater as the absorbing solution.
The gas supply apparatus 13 is disposed such that the gas jetting
direction is along the tangential direction of the peripheral wall
area 11a of the absorption tower main unit 11. Therefore the
exhaust gas introduced from the gas supply apparatus 13 is injected
in the horizontal direction along the inner circumference surface
of the peripheral wall area 11a. The position of the gas supply
apparatus 13 is not limited to the position lower than the region
where the spray apparatus 12 sprays liquid, as illustrated in FIG.
2B, but may be at a same height as the spray nozzle 12d which is
located in a position lower than the spray apparatus 12. In this
case, the length of the reaction area can be secured without
decreasing the removal rate of the toxic substances in the exhaust
gas, therefore the height of the absorption tower main unit 11 can
be decreased.
The liquid returning member 14 includes: a turn-back surface area
14a that circularly protrudes from the peripheral wall area 11a of
the absorption tower main unit 11 toward the center axis; a bent
piece 14b that is bent down from the edge of the turn-back surface
area 14a on the center axis side; a liquid collecting wall 14d that
protrudes upward from the edge of the turn-back surface area 14a to
form a liquid reservoir 14c; and an opening 14e that allows the
liquid collected in the liquid reservoir 14c to fall through.
A region on the center axis side surrounded by the bent piece 14b
and the liquid collecting wall 14d of the liquid returning member
14 installed in the absorption tower main unit 11 constitutes an
opening 14g (see FIG. 2B). This opening 14g is configured to have
an inner diameter that is 50% to 80% of the inner diameter of the
opening 11c of the absorption tower main unit 11. By this
configuration, pressure loss, due to the installing the liquid
returning member 14 in the absorption tower main unit 11, can be
suppressed.
The baffle 15 is constituted by a disk part 15a and a leg part 15b
that connects the disk part 15a to the peripheral wall area 11a of
the absorption tower main unit 11. A gap that allows droplets to
flow through is formed between the outer periphery of the disk part
15a and the peripheral wall area 11a of the absorption tower main
unit 11. The baffle 15 divides the inside of the absorption tower
main unit 11 into a region where the spray apparatus 12 sprays
liquid and a region where liquid, to be drained from of the
absorption tower main unit 11, is stored. A drainage pipe 16, to
drain liquid from the absorption tower main unit 11, is disposed in
a location below the baffle 15.
Next the exhaust gas treatment in the scrubber 10 configured like
this will be described. The exhaust gas discharged from the engine
is introduced by the gas supply apparatus 13 to a position lower
than the region where the spray apparatus 12 sprays liquid. This
exhaust gas rises inside the absorption tower main unit 11 while
circling along the peripheral wall area 11a.
Seawater, on the other hand, is introduced into the conduit 12b via
the feed pipe 12a. Then the seawater is sprayed from the spray
nozzles 12d disposed in the plurality of branch pipes 12c, toward
the peripheral wall area 11a of the absorption tower main unit
11.
Therefore the exhaust gas that circles and rises inside the
absorption tower main unit 11 contacts with seawater sprayed from
the spray nozzle 12d installed in each branch pipe 12c disposed at
each level, and the sulfur dioxide in the exhaust gas is absorbed
and removed. The exhaust gas, from which the sulfur dioxide has
been removed, is exhausted into air through the opening 11c, which
is formed in the upper portion of the absorption tower main unit
11.
The sprayed seawater, which becomes droplets, is forced against the
peripheral wall area 11a by the centrifugal force due to the
circling and rising flow, and drips down by its own weight. However
a part of the seawater rises inside the absorption tower main unit
11 by the circling and rising flow.
The gas flow rate of the center portion of the absorption tower
main unit 11 is a 0 m/s or neighborhood value thereof, and the gas
flow rate is faster in an area near the peripheral wall area 11a
compared with the center portion, therefore the seawater rises
along the peripheral wall area 11a by the centrifugal force. The
seawater that rises along the peripheral wall area 11a is
interrupted by the liquid returning member 14 at the lowest level,
and is collected in an area around the lower surface of the
turn-back surface area 14a and the bent piece 14b. If the collected
liquid reaches a certain amount, the liquid becomes droplets and
drips down by its own weight.
A part of the seawater, however, does not become droplets but rises
beyond the bent piece 14b, along the inner circumferential surfaces
of the bent piece 14b and the liquid collecting wall 14d of the
liquid returning member 14 by the centrifugal force, and rises
further along the peripheral wall area 11a between a liquid
returning member 14 and a liquid returning member 14. The seawater
that reaches the liquid returning member 14 at the next level is
interrupted by this liquid returning member 14, and is collected in
an area around the lower surface of the turn-back surface area 14a
and the bent piece 14b. If the collected liquid reaches a certain
amount, the liquid becomes droplets and drips down by its own
weight. These droplets are collected in the liquid reservoir 14c on
the lower level, and the collected liquid that exceeds a certain
amount falls into the lower portion of the absorption tower main
unit 11 via the opening 14e.
The gas flow rate of the area around the peripheral wall area 11a
of the absorption tower main unit 11 is faster compared with the
center portion of the absorption tower main unit 11, which means
that if the opening 14e is formed near the peripheral wall area
11a, the droplets may not fall via the opening 14e due to the
influence of the ascending current. Therefore the opening 14e is
formed in a position distant from the peripheral wall area 11a
where the gas flow rate is slower compared with area near the
peripheral wall area 11a, whereby the influence of the ascending
current is weakened, and droplets are allowed to fall through via
the opening 14e.
The liquid returning member 14 is disposed in a plurality of levels
in the vertical direction, which means that the rise of seawater by
the liquid returning member 14 is interrupted a plurality of times.
As a result, an out flow of the rising seawater through the opening
11c of the absorption tower main unit 11 can be effectively
prevented.
Further, even if the liquid returning member 14 is installed in the
absorption tower main unit 11, a pressure loss, caused by the
installation of the liquid returning member 14, can be lessened
since the liquid returning member 14 circularly protrudes from the
peripheral wall area 11a of the absorption tower main unit 11
toward the center axis, and the opening 14g is formed on the center
axis side. Moreover, clogging does not occur because of the liquid
returning member 14, which makes troublesome maintenance
unnecessary.
The droplets that are dripping down stop circling because the
baffle 15 is disposed in a lower area of the absorption tower main
unit 11, the droplets then fall down along the baffle 15 and the
peripheral wall area 11a, and are collected in the liquid reservoir
constituted by the bottom wall area 11b and the peripheral wall
area 11a of the absorption tower main unit 11. The collected liquid
is drained from the absorption tower main unit 11 via the drainage
pipe 16.
Now the configuration of the exhaust gas treatment apparatus
according to the present embodiment will be described in concrete
terms with reference to FIG. 3. FIG. 3 is a diagram depicting a
configuration of the exhaust gas treatment apparatus according to
the present embodiment.
As illustrated in FIG. 3, the exhaust gas treatment apparatus 100
is constituted by a plurality of (three in the case of this
embodiment) scrubbers 10 (10a, 10b and 10c).
An exhaust gas passage (second passage) 101a (101b, 101c), to
introduce exhaust gas into the scrubber 10a (10b, 10c), is
connected to the gas supply apparatus 13 of the scrubber 10a (10b,
10c). A switching valve 102a (102b, 102c), to switch the exhaust
gas passage 101a (101b, 101c), is disposed in the middle of the
exhaust gas passage 101a (101b, 101c).
The switching valve 102 (102a, 102b, 102c) can be configured using
a gate valve, a bell value or a butterfly valve. A butterfly valve
is particularly desirable for the switching valve 102 (102a, 102b,
102c).
A feed passage (first passage) 103a (103b, 103c), to supply liquid
to the spray apparatus 12, is connected to the feed pipe 12a of the
scrubber 10a (10b, 10c). Seawater from a seawater tank 106 is
supplied to the feed passage 103 (103a, 103b, 103c) via a seawater
pump 107.
Depending on the sea area where the ship is traveling, the seawater
discharged from the scrubber 10 may not be allowed to drain into
the sea due to maritime regulations. In this case, the seawater
supplied from the scrubber 10 to a later mentioned drainage passage
105 could be stored in the seawater tank 106 as circulation
seawater, and used for the exhaust gas treatment again.
In the case of the circulation seawater, however, alkali components
in the seawater have been consumed by the scrubber 10 that has
absorbed SO.sub.2. Therefore the absorption reaction of SO.sub.2 in
the exhaust gas with the seawater may be interrupted in the
repeated exhaust gas treatment, and as a result, SO.sub.2
concentration in the treated exhaust gas, which is discharged from
the scrubber 10 into air, may exceed the emission control
value.
Hence to compensate for the absence of alkali components in the
seawater, the feed passage 103 is configured such that alkali
agents can be injected from an alkali tank 108 via an alkali pump
109. A sodium hydroxide (NaOH) solution can be used for the alkali
agent.
In the middle of the feed passage 103a (103b, 103c), a switching
valve 104a (104b, 104c), to switch the feed passage 103a (103b,
103c), is disposed. The switching valve 104 (104a, 104b, 104c) can
be configured using a gate valve or a ball valve.
The switching valves 102 and 104 can be configured as a manual
type, an electromagnetic or electric type, or a compressed air
driven type. It is preferable, however, that the switching valves
102 and 104 are constituted by an electro-magnetic or electric
type, or a compressed air driven type, and a compressed air driven
type is most desirable in terms of explosion prevention.
The switching of the switching valves 102 and 104 is controlled by
a control signal outputted by the controller 110. The controller
110 computes and outputs the control signal based on the engine
load instruction value. Because of this configuration, exhaust gas
can be treated using all the scrubbers 10 when the engine load is
at the maximum, and a number of scrubbers 10 used for the exhaust
gas treatment can be decreased as the engine load decreases.
A drainage passage 105 is connected to the drainage pipe 16 of the
scrubber 10a (10b, 10c). The seawater discharged from the scrubber
10 to the drainage passage 105 is either drained into the sea or
stored in the seawater tank 106 as circulation seawater.
In the exhaust gas treatment apparatus 100, a plurality of
scrubbers 10 are installed in parallel, which causes a problem of
equi-distribution when exhaust gas is introduced. However about 500
Pa of pressure loss is generated at the gas inlet of the gas supply
apparatus 13 of the scrubber 10, therefore no special consideration
is required. If the pressure loss of the scrubber 10 is decreased,
piping distribution that can implement equi-distribution of the
exhaust gas should be appropriately designed.
A plurality of scrubbers 10 are installed in parallel in the
exhaust gas treatment apparatus 100, which causes a problem of
equi-distribution when an absorbing solution is introduced. However
about 0.05 to 0.2 MPa of pressure loss is generated at the
absorbing solution inlet of the feed pipe 12a of the scrubber 10,
therefore no special consideration is required.
If the scrubber 10 is installed to treat exhaust gas discharged
from a ship engine, a combustion engine of a boiler or the like,
the relationship between the height and the diameter of the
scrubber 10 is designed so that the height becomes 7 m or less,
preferably 5 m or less. If the scrubber 10 is installed on the deck
of a ship, however, the height can be 10 m or more.
If the SO.sub.2 removal rate demanded for the scrubber 10 is 98%,
the scrubber 10 should be designed so that the flow rate of the
exhaust gas in a standard state (0.degree. C., 1 atm, DRY) becomes
6 m/s or less, preferably 3 m/s or less.
If the SO.sub.2 removal rate demanded for the scrubber 10 is 90%,
the scrubber 10 should be designed so that the flow rate of the
exhaust gas in a standard state (0.degree. C., 1 atm, DRY) becomes
10 m/s or less, preferably 6 m/s or less.
The retention time of the exhaust gas in the absorption tower main
unit 11 of the scrubber 10, that is, the retention time of the
exhaust gas in an area for the height of the absorbing solution
spraying region, to be more precise, should be 0.2 seconds to 2
seconds, preferably 1 second.
The amount of seawater that is supplied from the feed passage 103
to the scrubber 10 should be an amount whereby the spray apparatus
12 can spray 0.5 to 1.5 times the chemical equivalent amount when 1
is the chemical equivalent amount to neutralize sulfur dioxide
(SO.sub.2) in the exhaust gas to be treated, and preferably an
amount whereby the spray apparatus 12 can spray 1.2 times the
chemical equivalent amount.
The scrubber 10 is constituted by a material which is resistant to
seawater and alkali solutions. For example, low coast iron [e.g.
SS400) can be used. Examples of seawater-resistant materials that
can be used are: a copper alloy (e.g. naval brass), aluminum alloy
(e.g. aluminum brass), a nickel alloy (e.g. cupronickel) and
stainless steel (e.g. SUS 316L material).
Now multi-tower control by the exhaust gas treatment apparatus 100,
illustrated in FIG. 3, will be described. In the exhaust gas
treatment apparatus 100, a number of scrubbers 10 to be operated
can be controlled by controlling the switching of the switching
valve 102 disposed in the exhaust gas passage 101, and the
switching valve 104 disposed in the feed passage 103 according to
the engine load rate.
In the multi-tower control in the exhaust gas treatment apparatus
100, the relationship between the engine load rate and a number of
scrubbers to be used is shown below. First to set the rated
condition, the scrubber 10 is designed based on an 85% engine load,
which is a standard maximum value.
In this scrubber 10, if the engine load rate becomes 85% to 100%
(overload operation), the flow rate of the absorbing solution to be
supplied to the scrubber 10 or the amount of alkali added to the
seawater is increased more than the rated condition, so as to
handle this state.
If the engine load rate is 0% to 30% or preferably 0% to 15%, it is
controlled such that a number of scrubbers 10 in operation becomes
one. If the engine load rate is 10% to 70% or preferably 10% to
55%, it is controlled such that a number of scrubbers 10 in
operation becomes two. And if the engine load rate is 40 to 100% or
preferably 50% to 100%, it is controlled such that a number of
scrubbers 10 in operation becomes three.
FIG. 4 is a graph depicting a relationship between the number of
scrubbers to be operated and an engine load or amount of exhaust
gas to be treated. In FIG. 4, the solid line indicates the
operating state of the scrubber 10, and the broken line indicates
the stopping state of the scrubber 10.
As shown in FIG. 4, only one scrubber 10 is in operation while the
engine load or the exhaust gas treatment amount is (X.sub.1) to
(X.sub.2), and if the engine load or the amount of exhaust gas
being treated exceeds (X.sub.2), the second scrubber 10 also starts
operation. If the engine load or the exhaust gas treatment amount
exceeds (X.sub.3), the third scrubber 10 also starts operation. If
the engine load or the exhaust gas treatment amount decreases from
(X.sub.3), the third scrubber 10 stops operation, and the engine
load or the exhaust gas amount decreases from (X.sub.2), and the
second scrubber 10 also stops operation.
FIG. 5 is a graph depicting a relationship between the flow rate
per scrubber and an engine load or amount of exhaust gas being
treated. In FIG. 5, the solid line indicates the operating state of
the scrubber 10, and the broken line indicates the stopping state
of the scrubber 10.
As shown in FIG. 5, only one scrubber 10 is in operation, while the
engine load or the exhaust gas treatment amount is (X.sub.1) to
(X.sub.2), and as the engine load or the exhaust gas treatment
amount increases from (X.sub.1) to (X.sub.2), the flow rate of the
first scrubber 10a increases accordingly. If the engine load or the
amount of exhaust gas being treated exceeds (X.sub.2), the second
scrubber 10b also starts to be operated. At this time, as the
second scrubber 10b to be operated, the flow rate of the first
scrubber 10a decreases. Thereby exceeding the capacity of the first
scrubber 10a and wasting the absorbing solution and power,
generating unnecessary expenses, can be prevented.
As the engine load or the amount of exhaust gas being treated
increases from (X.sub.2) to (X.sub.3), the flow rate of the first
scrubber 10a and the second scrubber 10b also increases. More
specifically, the flow rate of the first scrubber 10a is increased
by the controller 110 to the upper limit value, thereafter the flow
rate of the second scrubber 10b is similarly increased.
If the engine load or the exhaust gas treatment amount exceeds
(X.sub.3), the third scrubber 10c also starts operation. At this
time, as the third scrubber 10c operates, the flow rate of the
second scrubber 10b decreases. As the engine load or the amount of
exhaust gas to be treated increases to more than (X.sub.3), the
flow rates of the second scrubber 10b and the third scrubber 10c
increase accordingly. More specifically, the flow rate of the
second scrubber 10b is increased by the controller 110 until it
reaches the upper limit value, and thereafter the flow rate of the
third scrubber 10c is similarly increased. When the amount of
exhaust gas to be treated reaches the maximum value that the
exhaust gas treatment apparatus can treat, the flow rate of the
third scrubber 10c reaches the maximum.
A case when the amount of exhaust gas being treated decreases from
the maximum value will now be described. As the engine load or the
amount of exhaust gas being treated decreases toward (X.sub.3), the
flow rate of the second scrubber 10b and the third scrubber 10c
decrease accordingly. More specifically, the flow rate of the third
scrubber 10c is decreased until the lower limit value by the
controller 110, thereafter the flow rate of the second scrubber 10b
is decreased by the controller 110. If the engine load or the
amount of exhaust gas being treated further decrease from
(X.sub.3), the third scrubber 10c stops operation. As the third
scrubber 10c stops operation, the flow rate of the second scrubber
10b increases.
As the engine load or the amount of exhaust gas being treated
decreases toward (X.sub.2), the flow rate of the first scrubber 10a
and the second scrubber 10b decrease accordingly. More
specifically, the flow rate of the second scrubber 10b is decreased
until the lower limit value by the controller 110, thereafter the
flow rate of the first scrubber 10a is decreased by the controller
110. If the engine load or the amount of exhaust gas being treated
further decreases from (X.sub.2), the second scrubber 10b stops
operation. And as the second scrubber 10b stops operation, the flow
rate of the first scrubber 10a increases.
As described above, according to the exhaust gas treatment
apparatus of the present embodiment, a plurality of scrubbers 10
are installed, and the exhaust gas to be treated is distributed to
the plurality of scrubbers 10, so that the removal rate of the
toxic substances in the exhaust gas can be increased in the entire
exhaust gas treatment apparatus 100, while keeping the diameter of
each scrubber to a predetermined value or less. Because of the
diameter of each scrubber is a predetermined value or less,
splashing of the absorbing solution can be suppressed. In this
embodiment, a number of scrubbers 10 in operation are controlled
based on the engine load or the amount of exhaust gas being
treated. However the present invention is not limited to this
embodiment. For example, the amount of the seawater sprayed by the
spray apparatus 12, instead of a number of scrubbers 10 in
operation, may be controlled based on the engine load or the amount
of exhaust gas being treated. Alternatively, both a number of
scrubbers 10 in operation and the amount of the seawater sprayed by
the spray apparatus 12 may be controlled, based on the engine load
or the amount of exhaust gas being treated.
Further, the installation locations of the scrubbers 10 in the
exhaust gas treatment apparatus 100 can be distributed, hence the
exhaust gas treatment apparatus can be installed in a location that
is subject to limited installation space, such as an engine room or
on the deck of a ship, and installability of the exhaust gas
treatment apparatus can be improved.
Moreover, the liquid to be supplied to the spray apparatus 12 of
the scrubber 10 and the gas to be introduced to the scrubber 10 can
be controlled by controlling the switching of the switching valves
102 and 104, therefore a number of scrubbers 10 in operation can be
changed depending on the combustion devices that generate exhaust
gas and the changes in the engine load. In other words, a number of
scrubbers 10 in operation can be adjusted according to the amount
of the exhaust gas to be treated, hence an energy saving operation,
without waste, is implemented.
Furthermore, a number of scrubbers 10 in operation and the amount
of the absorbing solution can be controlled according to changes in
the engine load or the like, hence appropriate spray properties can
be maintained.
According to the scrubber 10 of this embodiment, the height of the
absorption tower main unit 11 can be lowered, which allows the
scrubber 10 to be installed in an engine room or on the deck of a
ship, hence installability of the scrubber 10 as the exhaust gas
treatment apparatus is improved.
Moreover, as the scrubber 10 becomes smaller, a number of members
used for the scrubber 10 can be decreased, which lowers the price
of the scrubber 10. Further, the pump power and maintenance costs
can be reduced by using a hollow conical nozzle as the spray nozzle
12d, which further implements price reduction.
The present invention is not limited to the embodiments, but
numerous modifications can be made. In the embodiments, the size
and shape illustrated in the accompanying drawings are not limited
to these, but may be modified appropriately within a scope in which
the effect of the present invention is demonstrated. The present
invention may be appropriately modified without departing from the
scope of the objects of the present invention.
* * * * *